Ethylene-vinyl alcohol copolymers (hereinafter, may be abbreviated as EVOH) are excellent in transparency, a gas barrier property, flavor retention, solvent resistance, oil resistance, and the like, and making good use of such properties, are used for wide use including various packaging containers, such as food packaging containers, fuel containers, medical product packaging containers, industrial chemical packaging containers, and agrochemical packaging containers. For production of such molded article, EVOH is often melt molded, and after that, is secondary processed. For example, stretching in an effort to improve mechanical strength and thermoforming of a multilayer sheet including an EVOH layer to make a container shape are widely carried out.
In recent years, there are increasing demands for stretching at a higher draw ratio and obtaining a molded article in a deeper drawing shape by thermoforming. Since EVOH is a resin having a high modulus of elasticity, there are also increasing demands for a resin having greater impact resistance. From such a situation, a resin is desired that is improved in impact resistance and secondary processability without decreasing performances, such as transparency, a gas barrier property, flavor retention, solvent resistance, and oil resistance, that EVOH originally has as much as possible.
Patent Document 1 describes modified EVOH obtained by reacting a monofunctional epoxy compound with a hydroxyl group of EVOH and describes that flexibility and secondary processability of the EVOH are improved. However, since the modified EVOH is obtained by reacting an epoxy compound with EVOH in a molten state, there have been problems of increasing production steps and rising production costs. Patent Document 2 describes a resin composition, containing the modified EVOH described in Patent Document 1 and unmodified EVOH, that is capable of improving stretchability, secondary processability, and the like without severely reducing the barrier properties and the transparency of the unmodified EVOH. Patent Document 3 describes a fuel container having a layer of the resin composition according to Patent Document 2.
Patent Document 4 describes a packaging material which has a layer of a composition having a plurality of endothermic peaks in a melting curve by DSC measurement, made by blending a plurality of EVOHs having different vinyl alcohol contents, and describes that it is excellent in a gas barrier property, mechanical properties, and processability. However, in this case, it has not been easy to manage both the gas barrier property and the secondary processability at a high level and it has also been unavoidable to decrease the transparency.
Patent Document 5 describes modified EVOH that is obtained by copolymerizing ethylene, vinyl acetate, and 3,4-diacetoxy-1-butene and then saponifying it, and in which 3,4-dihydroxy-1-butene units are copolymerized, and describes that the modified EVOH is excellent in stretchability, a gas barrier property, appearance, and strength. However, since 3,4-diacetoxy-1-butene has the polymerization reactivity that is equivalent compared with vinyl acetate, most of it turns out to remain after polymerization when the copolymer is taken out at a low conversion. Therefore, loads of washing and wastewater treatment increase and a rise in production costs is also unavoidable.